What is termed “3-D observation” is achieved by displaying left and right images (i.e. images having different parallax) to only the left eye and right eye, respectively, of a viewer. Usually, this requires that the viewer wear glasses or the like in order for the left eye to see only images intended for the left eye, and for the right eye to see only images intended for the right eye. However, the wearing of glasses and the like to achieve 3-D viewing effects is troublesome. There do exist prior art 3-D display devices that do not require the viewer to wear glasses in order to keep the images intended for the left eye from being visible to the right eye, and vice-versa. However, in these prior art 3-D display devices, a wide field angle and large eye relief cannot be achieved simultaneously, due to physical interference between the left and right optical systems and the left and right optical elements.
Electronic image display devices include face mounted displays (FMD's), head mounted displays (HMD's) and television monitors. Small electronic image display viewing devices, such as currently developed FMD's and HMD'S, can provide a viewer's left and right eye with separate images having different parallax using left and right optical viewing systems, respectively, that are placed very near the eyes.
Recently, an improved display structure has been developed. Japanese Patent Publication No. 2000-338412 ensures a maximum effective aperture for an optical system by bonding left and right optical magnifying systems to a display surface. The left and right images are prevented from entering the right and left eye, respectively, by reason of the exit pupils of the left and right optical magnifying systems being separated. However, even with this improvement, a wide field angle and a large eye relief are not simultaneously achieved.
Another conventional solution uses a monitor. Left and right images are displayed alternately on the monitor and means are provided to separately convey these images to the respective intended eyes of the viewer. There also are other means that are used for selectively displaying images with different parallax to the left and right eyes, respectively, so as to achieve a 3-D observation. Typically, the viewer wears glasses having a shutter mechanism for switching between the left and right eyes. The shutter mechanism is synchronously timed to the left and right images that are displayed, so that the left eye receives only the left images and the right eye receives only the right images. However, this also requires the viewer to wear glasses. Further, the viewer should be some distance from the display device in order for it to be comfortable to view, resulting in a larger display device.
Further, Japanese Patent Publication No. 2000-267045 provides a structure for displaying 3-D images that does not require the user to wear glasses. The display device includes an optical system in which left and right images independently reach the left and right eyes, respectively. However, a lens surface is required to be located at the screen for projecting the images. Yet, no other optical system is required between the screen and the viewer's eyes. The viewer's eyes should be at least 300 mm, and preferably 1000 mm, away from the display device for comfortable observation, resulting in a large device.